398 THE HUMAN BODY. 



spiratory discharges and diminish that to expiratory, and 

 are stimulated when the lungs expand. Hence, every ex- 

 pansion of the lungs (inspiration) tends to promote an 

 expiration, and every collapse of the lungs (expiration) tends 

 to produce an inspiration; and so, through the pneumo- 

 gastric nerves, the respiratory mechanism is largely self- 

 regulating. 



Asphyxia. Asphyxia is death from suffocation, or want, 

 of oxygen by the tissues. It mav be brought about in 

 various ways; as by strangulation, which prevents the entry 

 of air into the lungs; or by exposure in an atmosphere con- 

 taining no oxygen; or by putting an animal in a vacuum; 

 or by making it breathe air containing a gas which has a- 

 stronger affinity for haemoglobin than oxygen has, and 

 which, therefore, turns the oxygen out of the red corpuscles 

 and takes its place. The gases which do the latter are 

 very interesting since they serve to prove conclusively that 

 the Body can only live by the oxygen carried round by the- 

 hasmoglobin of the red corpuscles; that amount dissolved 

 in the blood plasma being insufficient for its needs. Of 

 such gases carbon monoxide is the most important and best 

 studied; in the favorite French mode of committing suicide 

 by stopping up all the ventilation holes of a room and 

 burning charcoal in it, it is poisoning by carbon monoxide- 

 which causes death. 



The Relations of Carbon Monoxide to Haemoglobin. 

 If aerated whipped blood, or a solution of oxyhfemoglobin, 

 be exposed to a gaseous mixture containing carbon mon- 

 oxide, the liquid will absorb the latter gas and give off 

 oxygen. The amount of carbon monoxide taken up will 

 (apart from a small amount dissolved in the plasma) be inde- 

 pendent of the partial pressure of that gas in the gaseous 

 mixture to which the blood is exposed; the quantity absorbed 

 depends on the quantity of haemoglobin in the liquid, 

 and is replaced by an equal volume of oxygen liberated. 

 This equivalence of volume, of itself, proves that the phe- 

 nomenon is due to the chemical replacement of oxygen 

 in some compound, by the carbon monoxide; for if the 

 carbon monoxide were merely dissolved in the liquid in 



